Using nitride-based III-V group compound semiconductors such as gallium nitride (GaN), there have been developed semiconductor light emitting devices such as high-intensity ultraviolet to blue and green light emitting diodes (LED) and blue-violet to blue and green laser diodes (LD).
These semiconductor light emitting devices are required to improve light emitting efficiency while suppressing an operating voltage.
JP-B 3427265 proposes the configuration of a nitride semiconductor light emitting device in which a layer including a base layer made of undoped GaN and an intermediate layer made of n-type impurity-doped GaN is provided between an n-type contact layer and n-type multilayered film layer with a view to improving light emitting efficiency and obtaining a preferable electrostatic withstand pressure.
In general, a gallium nitride semiconductor light emitting device is formed on, for example, a sapphire substrate and generates compressive stress in an epitaxially grown layer due to a difference in coefficients of thermal expansion between the substrate and the epitaxially grown layer. This compressive stress causes an accumulation of distortions in a quantum well layer of an active layer, for example. As a result, the influence of piezoelectric field becomes obvious, which prevents a light emitting output from being improved. Therefore, there is a room for improvement in terms of stress relaxation.